The biological consequences which follow the interaction of a DNA reactive chemical with its substrate are a function of an extremely complex balance of events which include the nature of the chemical, its activation status relative to reactivity with DNA, the DNA repair competence of the cell, where in the genome the damage occurs and the replication status of the cell. A further complicating feature of this problem concerns the multiplicity of DNA adducts which can be produced by a single chemical compound. Thus the relationship between an initial DNA damaging event and the final or measured biological end point is extremely complex. An approach to reduce the complexity of this latter issue is to restrict the spectrum of lesions which are formed in DNA to a single, well characterized adduct. This proposal focuses on the introduction of a single DNA adduct within an oligonucleotide into a defined site within a reporter gene for a bacteriophage vector. When this specifically modified vector is introduced into E. coli, the biological fate of that altered base will be evaluated in regard to a) the frequency and spectrum of mutations, b) adduct-associated phage inactivation, c) the DNA repair status of the cell, and d) the effect which active transcription may have on adduct processing.